Thallium triiodide

Chembox new
Name = Thallium triiodide
ImageFile =
ImageSize = 200px
ImageName = Thallium triiodide
IUPACName = thallium(I) (triiodide)
OtherNames = thallous triiodide
Section1 = Chembox Identifiers
CASNo = 60488-29-1
Section2 = Chembox Properties
Formula = TlI₃
MolarMass = 585.097 g/mol
Density =
MeltingPt =
BoilingPt =

Thallium triiodide is a chemical compound of thallium and iodine with formula TlI₃. Unlike the other thallium trihalides, which contain thallium(III), TlI₃ is a thallium(I) compound and contains the triiodide ion, I₃⁻.An appreciation as to why Tl⁺ is not oxidised to Tl³⁺ in the reaction::Tl³⁺ + 2I⁻→ Tl⁺ + I₂can be gained by considering the standard reduction potentials of the half cells which are:

:Tl³⁺ + 2e→ Tl⁺ ; E_r^o = 1.252:I₂ + 2e→ 2I⁻ ; E_r^o = 0.5355;

The favoured reaction is therefore the reduction of Tl³⁺ (1.252 > 0.5355).

It should be noted that using standard electrode potentials in this way must be done with caution as factors such as complex formation and solvation may affect the reaction. TlI₃ is no exception as it is possible to stabilise Tl^III with excess I⁻ forming the TlI₄⁻ ion.

tructure and preparation

TlI₃ is formulated Tl⁺ I₃⁻, and has a similar structure to NH₄I₃, CsI₃ and RbI₃. [ "Die Kristallstrukturen von Rubidiumtriiodid und Thalliumtriiodid" Tebbe K.F., Georgy U Acta Crystallographica,C (1986) 42, 1675 doi:10.1107/S0108270186090972] The triiodide ion in TlI₃ is nearly linear but is asymmetric with one iodine−iodine bond longer than the other. For comparison the dimensions of the tri-iodide, I_a−I_b−I_c, ions in the different compounds are shown below:

TlI₃ can be prepared by the evaporation of stoichiometric quantities of TlI and I₂ in concentrated aqueous HI, or by reacting TlI with I₂ in ethanol.

General references

* [http://www.webelements.com/ WebElements]
*Greenwood&Earnshaw

Footnotes